We always rent from Alamo but this time the rates are really high. What rental agencies on at the airport, we don't want to take a shuttle for an off site place.
I believe all of them are on-airport, you just walk across to the ramp. I know we've rented National, Budget, Hertz, Enterprise...maybe others. All have been just a walk out the door.
If you are staying on property you can take Magical Express. Alamo/National can be rented at the Dolphin and car care center. They will pick you up and shuttle you to their sites.
If things haven't changed the rate will be cheaper. When you rent at the airport an airport tax is added. Been awhile since I rented.